A SiAlON has a structure in which aluminum (Al) and oxygen (O) are dissolved in silicon nitride (Si3N4) in a solid state. Normally, for the SiAlON, there have been known the following two types of crystalline structures: α-SiAlON and β-SiAlON, both of which belong to a hexagonal crystal structure. A SiAlON-based sintered material employing such a SiAlON has low reactivity with a metal and therefore has been developed as a material for cutting tools.
Each of Japanese Patent Laying-Open No. 2011-121822 (Patent Document 1) and Japanese Patent Laying-Open No. 2011-140415 (Patent Document 2) proposes a sintered material containing a cubic SiAlON (hereinafter, also referred to as “c-SiAlON”) having a hardness higher than those of the α-SiAlON and the β-SiAlON in order to improve wear resistance when the sintered material is used as a cutting tool. Further, it has been known that titanium nitride (TiN) also exhibits very excellent wear resistance with respect to a heat-resistant alloy.